An active magnetic bearing (AMB) is used, for example, in a turbo compressor. Because of the special characteristics of turbo compressors and the special characteristics of the magnetic bearings, the following problems can occur: Depending on the aerodynamic design of the turbo compressor, in the specified operating range of the latter, disturbing forces can be exerted on the rotor by aerodynamic phenomena, resulting in unacceptably severe mechanical oscillations (oscillations with high oscillation amplitudes). In order to protect the turbo compressor against damage, the turbo compressor is shut down in the event of impermissibly severe mechanical oscillations.
As compared with oil-lubricating bearings, magnetic bearings have a lower bearing stiffness. A relatively low bearing stiffness benefits the occurrence of mechanical oscillations with high oscillation amplitudes. This applies in particular in the case of disturbance forces with a low disturbance frequency (excitation frequency). For example, the known flow phenomenon “rotating diffuser stall” meets the above-described conditions and, in turbo compressors with magnetic bearings, can lead to mechanical oscillations with impermissibly high amplitudes.